The present invention broadly relates to a tensioning and connecting apparatus for connecting overlapping strap ends of synthetic or thermoplastic material tensioned around at least one package or article to be wrapped and possessing a frictional welding device located ahead or forwardly of a tensioning device as seen in the direction from which tension is applied.
In its more particular aspects, the tensioning and connecting apparatus of the present invention comprises a friction welding device possessing a clamping ram or shoe positioned above a gap for accommodating the mutually overlapping ends of the band or strap. A welding element comprising a jaw or tongue is positioned below the gap and opposite to the clamping shoe and, by vibrating or oscillating, generates frictional heat. A retention device is capable of engaging with or holding the tensioned mutually overlapping ends of the band or strap.
In other words, the tensioning and connecting apparatus of the present invention is for tensioning and connecting mutually overlapping ends of a strap of synthetic material and comprises a tensioning device defining a direction of tensioning, a friction welding device arranged ahead or forwardly of the tensioning device in the direction of tensioning, and means defining a gap for accommodating the mutually overlapping ends of the strap. The friction welding device comprises a clamping shoe arranged above the gap. A welding element is arranged opposite the clamping shoe beneath the gap and is oscillated in relation to the clamping shoe for generating frictional heat. A retention means is provided for retaining the strap in a tensioned state.
A known manually operated or hand-operated tensioning and connecting apparatus of the initially mentioned type is known from the Swiss Pat. No. 637,587, granted Aug. 15, 1983, and serves for wrapping or banding a package or article or a number of articles which are to be bundled or jointly wrapped with a band or strap of thermoplastic material serving as a ligature. To apply tension to the band or strap, this known tensioning and connecting apparatus possesses a tensioning wheel which engages with the surface of the band or strap and is coupled to an electric motor or pneumatic motor by means of a dog clutch or coupling. After the tensioning procedure has been accomplished, the dog clutch or coupling is released so that the tensioning wheel remains stationary. In order to maintain tension in the strap after the dog coupling is released, a band or strap clamping device of the tensioning and connecting apparatus serves as a bolding or retention mechanism by engaging with both of the overlapping strap ends. This band or strap clamping device is located ahead of
This band or strap clamping device is located ahead of the welding or connecting device as seen in the direction from which tension is applied. Both ends of the strap are under tension in the vicinity of the welding device. In order to obtain sufficient relative motion between both strap ends to produce a frictional weld despite the tension applied, both the outermost strap end and the innermost strap end are set into motion. These overlapping strap ends are pivoted or rotatively oscillated about a pivot axis which lies in the center of the welding spot.
The generation of relative motion is hindered when the strap is tensioned and laterally held. Therefore it is to be noted that in the initially mentioned type of tensioning and connecting apparatus, the possibility exists of lifting the tensioning wheel from the strap during the welding operation. In this way the lateral blockage of the outermost strap end, which is still connected with the supply reel, is at least partially neutralized or nullified in one direction of the strap. The innermost strap end, however, remains tensioned and laterally held in the vicinity of the welding device between the strap clamping or retention device and a tensioning shoe. To overcome the ensuing hindrance, the drive motor of the welding device must be designed with sufficient power output or performance. Since the same motor also serves to drive the tensioning wheel, it is necessary to take into consideration the power or torque requirements of the tensioning wheel when designing the motor. Other than the costs associated with a powerful motor, there is no practical difficulty in adequately and sufficiently designing a motor for operation from an electrical power supply network or from a compressed air source or pneumatic network. The design of such a tensioning and connecting apparatus for operation independently of such a network presents the difficulty that the batteries necessary for such power requirements would exceed the size and weight limitations of a manual device.
A further disadvantage of the initially mentioned type of tensioning and connecting apparatus is that only limited tensioning force can be applied by the tensioning wheel due to the risk of possible damage to the strap. This limited tensioning force is not adequate for certain applications, for example, for wrapping or binding together objects such as panels or pipes having long, smooth surfaces.
A further known tensioning and connecting apparatus of the initially mentioned type is known from the West German Patent Publication No. 3,200,951, published Apr. 14, 1983. This apparatus applies tension to a strap by means of a tensioning or gripping jaw which engages the surface of the strap and is driven or actuated by an eccentric mechanism. The strap is held by a retention jaw which is positioned directly in front of the tensioning or gripping jaw and which substantially prevents backward slippage or return. The welding device of this tensioning and connecting apparatus, as seen in the direction from which tension is applied, is positioned subsequent to the tensioning device and comprises a pivotably mounted jaw which engages with the outermost strap end and is pivotable transversely to the longitudinal axis of the strap. The outermost strap end lies between the tensioning element and the supply reel during the welding operation. Its freedom of movement is thus impaired and the drive motor of the welding device must therefore be designed to have sufficient power capacity or performance. Applying tension by means of a tensioning or gripping jaw is burdened with essentially the same disadvantages as applying tension by means of a tensioning wheel.